Discoid meniscus
A discoid meniscus (Latin Meniscus disciformis ) is an anatomical variant of the menisci of the knee joint. The discoid meniscus was first described in 1889 by RB Young.
The discoid meniscus and its investment is innate, partly on both sides. The assumption that the discoid meniscus is absent the formation of sickle from the disk form embryologically scale, has been ruled out by histological studies on embryos. It was during the whole embryonic period no discoid meniscus forms are detected, so that rather mechanical failure loads of menisci with greater variability for the training of discoid be held responsible. Complaints (symptoms ) caused by a discoid meniscus only when under load on the knee joint, the central portion of the meniscus between the femoral condyle ( femoral condyle ) and tibial plateau ( tibia ) pinches and is moved, resulting in a classic snap - phenomenon and pain. These symptoms begin until around the age of 6 to 8 years of age due to the body size and body weight of children. In very few cases, the symptoms occur much earlier on, but rarely, even after the age of 12. The belated recognition of typical discoid meniscus discomfort is often due to the rarity and thus the ignorance of many physicians about the disease and its characters. To secure that finding, especially the magnetic resonance imaging investigation is. A treatment is indicated only when complaints and consists in a partial removal of the discoid meniscus.
The normal meniscus
The two normal menisci of the knee joint run as triangular fibrocartilage disks each inside and outside in the main joint between the thigh rolls and tibial plateau as the elastic pressure cushion with base on the joint capsule. The articular surfaces of the femoral and tibial roles are not congruent, that is, they do not affect a large area, but only selectively. This incongruity of the joint surfaces of the knee joint is balanced by the menisci. The meniscus area increases at the joint load to a substantial part of the load in the edge areas, and outputs it to the opposing articular surface on. Thereby, the forces acting on the articular surfaces are distributed over substantially larger areas and therefore relatively decreases. This cartilage- protective effect of normal menisci becomes clear if due to illness or injury, a meniscus is surgically removed. After a short time it comes to overuse injuries of the articular cartilage, and the image of osteoarthritis.
Anatomy and structure of the discoid meniscus
For a better understanding of the clinical picture disk meniscus contributes a widely accepted classification of the variations of the lateral meniscus Watanabe classification. Discoid type 1 and 2 have the same position within the knee joint as normal menisci, are thus connected to the joint capsule with its base. Only its form is not triangular, but they have the form of a complete or incomplete disk that the two joint surfaces of the bones involved completely separated from each other due to their position - similar to an articular disc, in the English language therefore referred to as discoid meniscus. Thus, the joint surfaces are in principle very well protected from cartilage wear, as long as the discoid meniscus causes no symptoms themselves. Type 3 discoid menisci are not characterized by their shape or thickness, but by their lack of attachment to the posterior joint capsule. Therefore, snap - phenomena are especially often expected.
Discoid menisci are found to vast numbers in the side ( lateral ) main joint of the knee, that is, between the lateral femoral condyle and the tibial plateau. Very rare to find discoid menisci in the inside ( medial ) joint space.
Discoid menisci can fill a different sized region of the hinge area between the base of the meniscus and the center of the joint to the tibial intercondylar. One speaks of complete ( type 1) or incomplete discoid menisci (type 2), the transition from a broad normal meniscus and a small discoid meniscus can be clearly seen from the fact that in the event of a discoid meniscus, the femoral condyle in the principal loading zone for arthroscopic assessment is not the opposite articular surface of the tibial plateau reached directly.
Discoid menisci have a high percentage (30 to 77%) of an unstable attachment to the joint capsule. A fundamental instability is the hallmark of type 3 discoid meniscus. The instability can be congenital or occur as a result of Meniskuseinklemmung as crack. Therefore particularly unstable menisci show an increased snap phenomenon.
But discoid menisci can be not only in its extent, but also in its substance, that is, differ in their thickness. So there are narrow, a few millimeters thick meniscus discs but also through more than 5 mm thick slices.
Pathology of the discoid meniscus
Because of its tissue composition as a fibrocartilage disc of the meniscus as the normal meniscus can withstand high compressive and shear stresses. With increasing body weight of the patient, it is, however, in the high -friction system articular cartilage - synovial fluid to adhere the meniscus to the joint surface. The cause is a compression effect of the body weight that is greater than the slipperiness between the meniscus and the articular surface. This adherence of the meniscus and the release of the short-term bonding leads to the characteristic snapping during articulation. By the " baking " of the meniscus surface on the joint surfaces, the two surfaces of the meniscus to be moved in knee flexion and extension in opposite directions, which leads to a rupture, and thus to the inner wear of the fiber fabric.
In continuation of the shear movement, it can then lead to superficial tears in the meniscus. Also, the discoid meniscus can tear off like a normal meniscus at its base to the joint capsule. A torn discoid meniscus lies in the joint not smooth on the cartilage- covered articular surfaces, but drumming up along the cracks and thus leads to local overloading of the articular cartilage. Overloading of the articular cartilage lead regardless of the cause ( increased body weight, joint stages after fracture, congenital or acquired Beinachs error, sports overload, incongruence and ligamentous instability ) in the long run to premature degenerative joint disease ( osteoarthritis ). Children and adolescents, in which discoid occur almost exclusively, develop osteochondritis dissecans herd as a result of regional congestion in unstable and torn menisci. Even the wily discoid meniscus may like normal menisci are pinched in the joint space while pulling on its attachment to the joint capsule, which creates pain.
Incidence
The frequency of discoid meniscus is difficult to determine because of the high number of asymptomatic patients. The values ranging from 0.4 to 17 percent of the lateral side, and 0.06 to 0.3 percent of the medial side. Other authors estimate the value to 1 to 3 percent of children and adolescents, with 10 to 20 percent of patients both knees are affected. In Asian countries, the incidence is obviously higher than in the Western world.
Diagnostics
Often the patients or their parents report a typical joint snapping when climbing stairs or walking. In most cases, this character has increasingly developed over the months and years before the performance. Severe pain does not exist. Temporary or permanent may occur joint blockages with extension deficit. In the investigation of patients snatching the joint can be reproduced in the functional examination. Many patients unfortunately, but also load-dependent non-specific knee pain without causing blockages. Rarely, joint effusions. The complaints are localized laterally at the level of the joint space due to the typical lateral ( side ) arranged discoid menisci.
X-ray examinations as well as bring blood laboratory tests no abnormal findings. Rarely can appear broadened in normal x-ray examinations, the lateral joint space. A reliable representation of discoid menisci can be found in the context of a magnetic resonance imaging study. Here, the disk of cartilage can be represented in its extent and thickness, as well as cracks in the normal tissues and fixation of the meniscus at its base.
Therapy
Arthroscopic partial resection
Discoid menisci, which are randomly determined at a magnetic resonance imaging for other indications will be left and not treated because they represent a perfect cartilage protection.
Clinically symptomatic discoid menisci that produce discomfort or an annoying snapping or produce pain even due to internal rupture of the tissue or complete tears of the menisci and damage joint cartilage need to be addressed surgically. The goal of surgery in addition to elimination of subjective symptoms such as pain, snap - phenomena and malfunction prevention of further joint damage and meniscal tears. Postponing surgery when an indication to do this is, the risk of joint damage increased sustainable. In the operation under an arthroscopy of the discoid meniscus of its central opening is cut ( at the tibial spine ) and then partially removed. Partial resection is the discoid meniscus is not simple: On the one hand, the lateral joint space in which typically is the discoid meniscus, already naturally very tight. On the other hand, can the lateral joint space not by a " release " of the outer band ( targeted Teilzerreißung the sideband ) expand as is done by default when operational difficulties in inner band. The lateral joint space is also through the thick discoid meniscus itself is filled ( see figure ). Working with mechanical surgical instruments is technically demanding in the narrow joint space in children. Therefore, often for the partial removal of the menisci next to the appropriate hand tools (punch ) usually motorized instruments (" shavers " ), or uses laser instruments or electrical so-called ablators. May have the RF devices (radio frequency ) devices and the laser but deeply damaging impact on the remaining meniscal tissue, and therefore should be the use of particularly the RF device caution. Some clinics use instead of the arthroscopic technique now back open accesses to the discoid meniscus. Decisive for the choice of the surgical procedure, the overview is reliable in the joint.
Great focus is the surgical treatment of a torn and dislocated complete discoid meniscus. Here take place, the repositioning of the past in the front recess meniscus made on the tibia joint surface, then the partial resection of the central portion of the meniscus and then the reattachment of the dorsal horn and the pars intermedia of the capsule. Importantly, the popliteal hiatus, the passage point of the popliteus tendon through the meniscus basis, this is not to close by the meniscal repair.
Partial resection should be used sparingly carried out only up to the point at which, with its main loading zone reaches the femoral condyle, the articular surface of the tibial plateau. A resection beyond this point is not recommended, since the protective effect of the meniscus on the articular surface is no longer given.
After partial resection of the discoid meniscus is a careful examination of the stability of the meniscus remnant with respect to the attachment to the joint capsule of the utmost importance. In cases of confirmed anterior, lateral or posterior instability suture fixation of the meniscal tissue is necessary. It can be either technically easier with arthroscopic suture apparatus, performed by suturing techniques from the inside out (inside- out) or by so-called all -inside technique (without exposing the capsule outside).
Open partial resection
Due to the narrow anatomy of the lateral ( lateral ) joint space and the resulting poor clarity of the operation area in the knee joint again open surgical techniques are described lately, which can be removed under direct vision with an open joint access the discoid meniscus. In the era vorarthroskopischen this procedure had been carried out by default.
Complications
Due to the narrowness of the lateral joint space and because of the filling of the joint space with the tissue of discoid meniscus cartilage superficial damage to the femoral condyle and tibial plateau on are hard to avoid in the surgical therapy. Using electrical ablation method or the laser, this damage can be kept small and can be compensated for by the body's own repair. In some cases, however, occur - possibly due to changes in damping situation after meniscectomy - damage to the lateral femoral condyle ( femoral condyle ), similar to osteochondritis dissecans (OD ): for example, clinical complaints in the form of load-dependent pain, see, for example, in sports and in MRI sign of subchondral ( located below the cartilage) necrosis of bone tissue. This damage can heal if necessary with relief of the affected leg. Sometimes, however, a surgical therapy is indicated.
Follow-up treatment
After arthroscopy is usually recommended a partial relief on crutches for a few days until the articular cartilage has normalized its enhanced by arthroscopy water content again. Then, the joint is stabilized by a velcro system for approximately two to three weeks in an extended attitude and can be loaded. Thus, the sparingly trimmed meniscus is further shaped by the Femurkondylenrolle, flattened at the edges and pushed to its position. Especially for additional suture fixation of unstable meniscal Share this stretch posture must be maintained to allow a replace it next of the meniscus to the capsule. In the following time free motion and load are allowed, but usually a sports ban is pronounced for two to six months. If after surgical therapy back discomfort can often have a magnetic resonance imaging show changes corresponding to an osteochondritis dissecans and how they must be treated.